The invention relates to a multi-head friction welding method for the concurrent welding of connecting surface areas of open or closed profile frames.
Friction welding methods as such are basically known wherein, by relative movement of two components under pressure, friction is generated so as to provide for the energy needed for melting the material at the surfaces to be welded together. The components to be welded together are generally linearly symmetrical or rotationally symmetrical. The procedure however is not suitable for the welding of asymmetrical components such as profile rods for profiled window or door frames.
For the manufacture of window and door frames of plastic profile rods, the surface areas to be joined are generally cut to the desired miter bevel and then welded together by a so-called mirror welding process. (DE-A-41 18 258). The concurrent welding of the miter areas of such profile frames using welding mirrors is known as multi-head compression butt welding wherein the surface areas to be joined are heated up to their melting point and are then, after removal of the mirrors, joined under pressure (DE-A-19 50 236). This multi-head pressure butt welding procedure has disadvantages particularly because of long processing times, that is, the time required for the heating and the melting, the joining and the hardening of the joint areas. Since the heat is dissipated from the joint area only slowly, the unavoidable large weld bulges formed in the process can be cut away only after a waiting period of several minutes. The removal of the bulges is furthermore quite complicated, particularly in the inner and in the corner areas. Finally, such multi-head pressure butt welding apparatus consume a relatively large amount of energy since the welding mirrors must be maintained continuously at operating temperature, also during the periods in which no welding takes place. Furthermore, oxidation layers are formed on the surface of the mirrors which must be removed for which procedure generally mirror envelopes of Teflon foils are used, which are quite costly.
It is therefore the object of the invention to provide a multi-head friction welding method and an apparatus suitable for performing the method whereby the disadvantages of the multi-head pressure butt welding method can be overcome and with which, at the same time, several or all the joint surface areas of profile frames consisting of profile rods can be welded at the same time and in shorter periods as compared with welding mirror processes and without the formation of large weld bulges.
This object is solved in accordance with the method and apparatus wherein the individual profile rods of the profile frames are firmly held in friction welding heads and the two surfaces to be joined are pressed against each other, the respective free ends of the profile rods at opposite sides of the jointure are caused to vibrate by means of the friction welding heads wherein the two friction welding heads vibrate 180xc2x0 out of phase in the X, Z and Y, Z direction and the friction welding heads receiving the free ends of each individual profile rods also vibrate essentially 180xc2x0 of phase. In order to generate the lowest possible amount of force vectors in the longitudinal direction of the profile rods, the two friction welding heads vibrate with a rigid phase relation 180xc2x0 out of phase.
With the process according to the invention, the manufacturing of profile frames becomes substantially more economical in that the processing times are substantially reduced. This is achieved in particular by short melt-on periods and short fitting and holding periods, which are generally in the area of one minute or substantially less. Since the process heat required is relatively low, the welding bulges are relatively small. The outer surfaces can therefore be finish-treated immediately after the welding procedure that is still during the holding or cool-down period, which is highly advantageous.
In order to eliminate an uncertain and non-reproducible welding procedure during the concurrent welding of the surface areas of profile frame members to be joined, the start-up of the friction welding heads is synchronized with start-up positions, which are 180xc2x0 out of phase and the phase angle between the oscillations of the friction welding heads are controlled during the welding procedure for accurate timing.
In a particularly advantageous embodiment of the invention, an ellipse-shaped vibration pattern is applied to the free ends of the profile rods. If, in a particular case of an elliptical vibration, a circular vibration is utilized, the conditions are particularly advantageous since, with the synchronization of the friction welding heads, the axially resulting force vectors along the engaged profile members can freely oscillate and no longitudinal forces are effective on the profile member engagement structures. As loading force on the profile, only the radical force remains with small resulting force vectors in the longitudinal direction of the profile rod so that, as a result of the 180xc2x0 phase displacement, an axially oscillating crank movement is achieved between the profile rod holding structures. No outwardly effective moments will occur.
The advantages of the invention also apply to the border case of an elliptical oscillation wherein one axis a or b of an ellipse approaches zero.
Particularly advantageous is the utilization of a multi-head friction welding method for the welding of door or window frames of plastic profile rods. In accordance with the invention, for this purpose, the door or window frames are positioned before the welding on a planar mounting surface such that the surface areas to be joined are disposed adjacent each other, that the friction welding heads are arranged with their profile member clamps at the ends of the profile rods adjacent the surfaces to be joined and are locked therewith during the welding procedure and the friction welding heads are shortly operated depending on the parameters: frequency of the oscillation, amplitude of the oscillation and engagement pressure for the concurrent introduction of the friction welding energy into all surface areas to be joined.
In such a case, with a square frame provided with two vibration heads at each miter joint or, respectively, jointure plane, and a 180xc2x0 out of phase oscillation and concurrent synchronization of the vibration heads, the force vectors can freely oscillation in the longitudinal direction of the profile rods held in position and no forces are effective on the profile clamps in the longitudinal direction of the profile rods. With the 180xc2x0 out of phase displacement, all rods oscillate in axial direction at the same time in a clockwise sense and then again in a counter-clockwise sense. Furthermore, a circular movement occurs at the opposite ends of each profile rod, which is opposite to that present at the end of the adjacent profile frame rod which experiences on opposite circular motion so that no outwardly free movements are effective with respect to the plane of jointure. The fact that, in this case, the free movements compensate each other is particularly advantageous for the friction welding method according to the invention.
For the welding of the surface areas to be joined of open or closed profile frames in accordance with the invention, a multi-head friction welding apparatus with several, preferably four, friction welding units, which are adjustably disposed on a machine bed, is utilized. Each friction welding unit consists of two friction welding heads with oscillating plates, which are firmly connected to clamping units. Each clamping unit includes a first clamping plate, which is movable relative to a second clamping plate for engaging a free end of a profile rod of the profile frame. The two friction welding heads assigned to a jointure plane are mounted with their clamping units on an assembly plate so as to be movable relative to each other in such a way that they are adjustable toward the jointure plane in accordance with the exact dimensions of the profile frame. For a proper positioning of the friction welding heads with respect to the angular position of the jointure plane, the assembly plates are supported on the machine bed in parallel guide structures and/or pivotal guide structures so as to be slidable and/or pivotable for position adjustment relative to the jointure plane.
Since, in accordance with the invention, the friction welding heads mounted on the assembly plate and the clamping units of the welding heads are slidably supported so as to be movable toward, and away from, the jointure plane and, furthermore, the position adjustment of the frame to be welded can be synchronized, the welding of the profile frame is facilitated while accurate dimensioning of the profile frame as desired can be achieved.
Since the profile rods of plastic material must not be exposed to excessive clamping forces because of the relatively thin webs disposed in the interior of the profile rods, metal support members are provided in accordance with the invention, which are 1/10 to 10/10 mm smaller than the clamping dimensions of the profile rod and which are added to the profile rod for limiting the clamping forces applied to a profile rod. The clamping unit connected to the oscillating plate of the friction welding head has a U-shaped reception area for the profile rod. A first movable clamping plate is disposed within the U-shaped reception area, whereby the clamping plate can be biased, by way of a profile clamping cylinder, preferably a pneumatic cylinder, vertically against the profile rod disposed in the respective clamping unit, while being supported by a leg of the U-shaped reception area, which leg forms a counter pressure surface.
Finally, the clamping unit preferably hasxe2x80x94in a top viewxe2x80x94the shape of a rectangular triangle, wherein the base of the U-shaped reception area extends normal to the jointure plane. With this clamping unit design, it is possible to engage in the clamping unit aligned profile rods as well as profile rods to be joined at almost any miter angle and ensure a relative position adjustment which is always normal to the jointure plane.
In order to be able to utilize the friction welding apparatus according to the invention for the welding of window frames, which have relatively short profile rodsxe2x80x94standard windows have a profile rod length of at least 26 cmxe2x80x94in accordance with the invention, the motor for the respective friction welding head drive is disposed in parallel with, and behind, the oscillation head and drives the oscillation head by means of a toothed belt. In this way, the two friction welding heads of two adjacent jointure planes can be positioned in close vicinity so that also the shortest commonly used profile rods can be welded together.
The advantages and features of the invention will become more readily apparent from the following description of an embodiment in connection with the accompanying drawings.